Well safety valve

ABSTRACT

A well safety valve closable by a predetermined flow rate including a housing connectible on a locking mandrel, inlet ports in the housing, a valve seat downstream from the ports, a pressure reducing flow bean in the housing downstream from the valve seat, a valve member in the housing upstream of the valve seat and engageable with the valve seat to shut off flow through the valve, an operator piston slidable in the housing and exposed on a first side to well pressure upstream of the valve seat, a piston rod secured from the piston to the valve member, an annular chamber within the housing around the piston rod, a pressure sensing tube on the valve member extending through the flow bean connecting with a passage in the piston rod opening into the annular chamber to apply fluid pressure from downstream of the flow bean to a second side of the piston for operating the piston responsive to a flow rate induced pressure differential, a spring in the annular chamber biasing the piston and rod in a direction to open the valve, a detent assembly between the housing and piston to insure valve closing without throttling, and a self-centering seal assembly around the piston rod within the housing sealing one end of the annular chamber.

United States Patent Dollison May 6, 1975 WELL SAFETY VALVE [57]ABSTRACT [75] inventor: William W. Dollison, Dallas, Tex. A well safetyvalve closable by a predetermined flow Assigneej Otis EngineeringCorporation, rate including a housing connectible on a locking DallasTex. mandrel, inlet portsm the housing, a valve seat downstream from theports, a pressure reduclng flow bean [22] Filed: Dec. 26, 1973 in thehousing downstream from the valve seat, a valve member in the housingupstream of the valve seat and [21] Appl' 428395 engageable with thevalve seat to shut off flow through the valve, an operator pistonslidable in the housing [52] US. Cl. 137/460; 137/498; 137/501 andexposed on a first side to well pressure upstream [51] Int. Cl. F16h17/02 of the valve seat, a piston rod secured from the piston [58] Fieldof Search 137/460, 461, 463, 464, to the valve member, an annularchamber within the 137/498, 501; 166/224, 224 S housing around thepiston rod, a pressure sensing tube on the valve member extendingthrough the flow bean [56] References Cited connecting with a passage inthe piston rod opening UNITED STATES PATENTS into the annular chamber toapply fluid pressure from 3,070,119 12/1962 Raulins 137/460 dfwnstreamof h flow to a secorld Side of the 3,126,908 3/1964 137/460 plston foroperating the piston responsive to a flow 3,138,174 6/1964 Gilpin137/498 rate induced pressure differential, a spring in the an-3,168,902 2/1965 Pearl 137/501 nu chamber biasing the piston and rod ina direc- 3,452,777 7/1969 Dollison 137/510 X tion to open the valve, adetent assembly between the 3, 68,506 10/1973 MC 37/ 98 X housing andpiston to insure valve closing without Garrett A throttling and aselfleentering ea] assembly around Primary Examinerl-larold W. WeakleyAttorney, Agent, or Firm-H. Mathews Garland the piston rod within thehousing sealing one end of the annular chamber.

9 Claims, 2 Drawing Figures WELL SAFETY VALVE This invention relates towell safety valves and more particularly relates to a well safety valveoperative re sponsive to a predetermined flow rate in a well.

In the operation of petroleum oil and gas wells, a condition may developwhich causes abrupt increases in the flow rates as a result of varioustypes of damage which may occur at the wellhead or along the tubing ofthe well. For example, physical destruction, particularly in offshorewells, may occur due to storms and the like causing the sudden openingof the wellhead resulting in a dangerous loss of fluids to thesurrrounding sea. While there are several styles or types of flow rateresponsive well valves available, they generally require flow rateswhich are substantial in volume and below which it remains possible forsevere damage to occur to a well resulting in leakage which does notcause the required flow rate to be developed to cause closing of thevalve. Also, the available valves have operating mechanism in the pathof fiow through the valve resulting in increased malfunction and flowcutting due to sand and trash.

It is a particularly important object of the invention to provide a newand improved form of safety valve.

It is another object of the invention to provide a well safety valvewhich is responsive to a predetermined flow rate in a well.

It is another object of the invention to provide a well safety valvewhich has an increased area over presently available valves exposed to apressure drop caused by the rate of flow through the valve.

It is another object of the invention to provide a well safety valvewhich provides maximum cross-sectional area for flow into the valve.

It is another object of the invention to provide a well safety valvewherein the major operating parts of the valve are located below theinlet ports of the valve away from sand and trash in the well fluid.

It is another object of the invention to provide a well safety valvehaving a self-centering seal assembly between the valve operating pistonrod and the valve housing.

In accordance with the invention there is provided a flow rateresponsive well safety valve having a valve housing provided with a borewith side ports spaced substantially from an open lower end of thehousing, a valve operating piston slidable in the bore, a piston rod, anannular valve member on the upper end of the piston rod, a valve seat inthe housing above the side ports engageable by the valve member forshutting off flow into the valve housing bore, an enlarged lower end onthe piston slidable in sealed relationship in the housing to provide awell pressure-responsive first area on the piston, an annular chamberbetween the piston and the valve housing, a side port in the piston rodopening into the annular chamber, a flow bean in the housing above thevalve seat, a pressure sensing tube on the piston extending through theflow bean for communicating downstream pressure from above the flow beanthrough the side port in the piston into the annular chamber around asecond area of the piston within the valve housing, a first spring inthe annular space between the housing and the piston biasing the valveopen, a detent system between the first spring and the piston forproviding a high energy resistance to valve closure and for biasing thevalve piston toward a valve open position when the detent system isactivated, a

second spring for biasing the valve piston toward an open position, andmeans for connecting the valve housing to a locking mandrel to supportthe valve in a well bore.

The foregoing objects and advantages together with the specific detailsof a preferred embodiment of the invention will be better understoodfrom the following description taken in conjunction with the drawingswherein:

FIG. 1 is a fragmentary longitudinal view in section and elevationillustrating a preferred form of well safety valve in accordance withthe invention, showing the valve open;

FIG. 2 is a view in section and elevation similar to FIG. 1 showing thevalve closed.

Referring to the drawings, a well safety valve incorporating thefeatures of the invention includes a valve housing 11, a valve operatorpiston 12, an annular valve member 13, a piston rod 12a between thevalve member and the piston, and a top sub and valve seat member 14threaded into the upper end of the housing. A pressure reducing flowbean 15 is supported in the sub above the valve member. A pressuresensing tube extends from the valve member through and above the flowbean. The housing is provided with side ports 21 to permit flow into thehousing and upwardly through the flow bean. The valve is biased open bya first detent spring 22 and a second main spring 23, and is closedresponsive to a flow rate induced pressure differential across thepiston 12 between the well pressure below the piston and a reducedpressure from above the flow bean sensed by the tube 20. The arrangementshown provides a large pressure-responsive area on the piston and entryof the fluids into the valve bore above the operating mechanism of thevalve.

The valve housing 11 is a tubular member having an enlarged head portion24 which is counterbored down to an internal upwardly facing shoulder 25and is internally threaded along an upper end portion for securing tothe lower end of the top sub and valve seat member 14. The enlarged headportion of the valve housing has a plurality of circumferentially spaceddownwardly opening milled slots the upper ends of which extend above thecounterbore shoulder 25 defining large lateral ports 21 into the bore ofthe head end of the housing for the admission of well fluids into thevalve. A bevelled seat surface 31 around the upper end of the valvemember 13 is engageable with a valve seat member 32 in the lower end ofthe sub 14 for shutting off flow through the valve from the side ports21.

The valve member is biased open by the springs 22 and 23 and is closedby the differential between the flow related reduced pressure above theflow bean and the well pressure around the valve. The springs 22 and 23are encased within the valve housing in an annular space 26 definedbetween the housing and the valve operating piston 12 and rod 12a. Thepiston rod 12a is formed integral with the valve member 13 and isthreaded along a lower end portion into the upper end of the piston 12which slides within the bore of the housing 11. The housing 11 has aninternal annular flange 35 forming a loose fit around the piston rod 33and defining an upwardly facing stop shoulder and a downwardly facingtapered stop shoulder 41. The spring 23 is contained within the annularspace 26 between the piston rod and housing compressed between thedownwardly'facing housing shoulder 41 and a ring 42 supported on theupper end edge 43 of the piston 12. The bore of the housing 11 isenlarged along a lower end portion 44 providing a downwardly facing stopshoulder 45 which limits upward movement of a spring retainer ring 50.The detent spring 22 is confined within the annular space 26 between thehousing and the piston compressed between the retainer ring and atubular detent ball retainer 51. The lower end edge of the ball retainer51 engages a plurality of detent balls 52 which latch and release thevalve operating piston depending upon the longitudinal position of thepiston in the housing. The piston head 12b of the piston 12 has anexternal upwardly tapered locking shoulder 53 which is engaged by theballs 52 at the longitudinal position of the operating piston shown inFIG. 1 coupling the detent spring 22 with the piston. The housing has aninternal annular detent ball release recess 54 which permits the detentballs to be cammed outwardly out of engagement with the shoulder 53 torelease the piston from the detent spring 22 during valve closure. Belowthe shoulder 53 the piston is further enlarged to a diameter forming asliding fit within the bore of the lower end portion of the housing 11.The piston head 12bis provided with an external annular recess 55 inwhich a ring seal is positioned for sealing between the bore wallsurface of the housing 11 and the piston head.

Spaced above the upwardly facing stop shoulder 40 on the flange 35 thehousing 11 is provided with an internal upwardly facing tapered stopshoulder 61 which is engageable by the tapered valve member surface 62limiting the downward movement of the valve member 13 and the operatingpiston and rod within the housing as illustrated in FIG. 1. Aself-centering seal assembly 63 is secured within the housing 11 abovethe internal flange 35 on the shoulder 40. The seal assembly is held inplace by a spacer ring 64 locked by a snap ring 65 engaged in aninternal annular recess within the upper end portion of the housing 11below the stop shoulder 61. The self-centering seal assembly includes aring having a lower end edge provided with a downwardly opening annularrecess in which an O-ring 71 is disposed for sealing between the ring 70and the housing flange shoulder surface 40. The ring 70 has an internalannular recess in which a ring seal 72 is disposed for sealing betweenthe ring 70 and the outer wall surface of the piston rod 33 below thevalve member 13. The outside diameter of the ring 70 is substantiallyless than the inside diameter of the bore portion 73 of the housingpermitting lateral movement of the seal assembly 63 within the housingto provide a self-centering feature as the rod 33 of the operatingpiston reciprocates through the seal during the opening and closing ofthe valve. Normal concentricity problems are eliminated by the sealassembly reducing manufacturing assembly costs.

The pressure sensing tube 20 is threaded along a lower end portion intothe upper end portion of a blind bore 74 drilled through the valvemember 13 into the upper end portion of the piston rod 12a. A side port75 in the piston rod communicates the bore 74 with the annular chamber26 within the housing around the piston rod so that pressure iscommunicated through the tube 20 and passage 74 from above the flow bean15 into the annular chamber above the piston head 12b. The seals 71 and72 seal the upper end of the chamber 26 and the seal 60 around thepiston head seals the lower end of the annular space. This featurepermits the fluid pressure downstream of the flow bean to be applied tothe operating piston above the seal 60 while well pressure is appliedover the head of the operating piston below the seal 60 providing a flowrate related pressure differential applied to the piston over an areadefined by the difference in the lines of sealing of the ring seal 60with the housing wall and the ring seal 72 with the piston rod 12a.

The sub 14 is counterbored along a portion defining an upwardly facinginternal annular stop shoulder 81 which supports the flow bean 15 withinthe sub. An O-ring seal 82 within an internal annular recess 83 in thesub seals between the sub and the flow bean. The lower end 84 of a lockmandrel body is threaded into the upper end portion of the sub 14 forsupporting the safety valve from the lock mandrel. The lower end edge 85of the lock mandrel body engages the upper end of the flow bean 15holding the bean in position in the sub 14. The lower end 84 may be thelower externally threaded end portion of the body of either an Otis TypeX Locking Mandrel as shown at page 3458 or an Otis Type S LockingMandrel as shown at page 3462 of the Composite Catalog of OilfieldEquipment and Services, 1972-73 Edition, published by World Oil,Houston, Tex. Either of these locking mandrels can be landed and lockedin an appropriate landing nipple included in a tubing string forsupporting the safety valve in the string. As shown in the refernces,these locking mandrels include external packing which seals around thelock mandrel within the tubing string above the safety valve 10 so thatany fluids flowing upwardly in the tubing string are directed into thesafety valve ports 21 when the valve is open.

In operation, the velocity safety valve 10 is connected with a suitablelocking mandrel such as the Otis Types X or S, is lowered by wirelineinto a well, and is locked at the desired landing nipple in the welltubing. The safety valve is normally open as illustrated in FIG. 1 heldby the combined forces of the springs 22 and 23. Thus, as the safetyvalve and locking mandrel are lowered such as by wireline, fluids in thewell may freely bypass the safety valve as it is lowered flowinginwardly into the valve housing through the side ports 21 and upwardlythrough the flow bean 15. With the safety valve landed and locked in thewall tubing, the valve remains open until well conditions produce avelocity through the valve sufficient to develop a pressure differentialwhich applies an upward force on the operating piston 12 of a value highenough to overcome the downward forces of the springs 22 and 23.

As the well fluids flow inwardly in the ports 21 and upwardly around thetube 20 through the flow bean 15 a pressure reduction is effected in thefluids as they pass through the flow bean. The valve is designed torespond to a pressure reduction which represents a flow rate in excessof predetermined safe limits for the well system in which the valve isinstalled. The pressure of the producing well fluids in the tubingaround the valve below the ports 21 is applied to the operating piston12 over an area defined by the line of sealing engagement of the ringseal 60 with the bore wall surface of the valve housing below. therecess 54. This force acts upwardly on the valve operator piston tendingto raise the valve member 13 upwardly toward the closed position on theseat 32 while the springs 22 and 23 bear downwardly on the valveoperator piston biasing the valve toward the open position of FIG. 1.The reduced pressure within the flowing well fluids caused by thepassage of the fluids through the restricted bore of the flow bean iscommunicated by the tube downwardly into the piston rod counterbore 74and laterally outwardly through the port 75. The reduced pressurecommunicated through the port 75 is transmitted within the annularchamber 26 around the operator piston 12 between the seal 60 at thelower end and the seals 71 and 72 at the upper end. The reduced pressuretransmitted through the tube 20 acts on upwardly facing surfaces of theoperator piston above the ring 60 to combine with the forces of thesprings 22 and 23 biasing the valve toward the open position. Theannular area on the piston and rod sealed by the ring seal 60 reduced bythe area sealed by the ring seal 72 defines the effective area actedupon by the fluid pressure differential biasing the valve closed. Whenthe flow rate of the well fluids upwardly in the well through the safetyvalve increases above the predetermined value for which the valve is setto close. the pressure differential acting over this defined area of thevalve operator piston produces an upward force on the operator piston inexcess of the downward force exerted by the springs 22 and 23 so thatthe valve operator piston with the valve member 13 begins movingupwardly. The springs 22 and 23 are simultaneously compressed. Thepiston head shoulder 53 lifts the detent balls 52 which raises the ballretainer 51 forcing the lower end of the detent spring 22 upwardlycompressing the spring. Simutaneously, the upper end edge 13 of thepiston 12 raises the retainer ring 12 lifting the lower end of andcompressing the spring 23. When the balls 52 are aligned with thehousing recess 54 the camming effect of the shoulder surface 53 forcesthe balls outwardly into the recess 54 at which positions the diameterof the piston 12 below the shoulder 53 may freely pass upwardly withinthe balls as shown in FM]. 2. At the moment that the balls 52 aredisengaged from the shoulder 53 the detent spring 22 is no longereffective to apply a downward force against the valve operator piston sothat the piston now moves upwardly against only the force of the spring23. While the resistance of the spring 23 increases as it is compressed, the pressure differential across the piston sufficient todisengage the spring 22 is great enough to force the operator piston andvalve member 13 upwardly in a snap action to the closed position shownin FIG. 2. Preferably, enough energy is stored in the upwardly movingvalve system for the valve to fully close without throttling when thedetent balls release the operating piston. The valve surface 31 on thevalve member 13 engages the valve seat 32 in the lower end of the uppersub 14 shutting off all upward flow through the valve.

When the valve 10 is closed as shown in FIG. 2, the well remains shut-inwith well fluid pressure in the tubing string below the valve actingupwardly to hold the valve closed while the only downward force on thevalve is that exerted by the spring 23 and any hydrostatic pressure offluids within the tubing string on the top of the valve member 13. Thedetent spring 22 is fully deactivated so long as the locking balls 52are held outwardly in the recess 54. The diameter of the piston head 343below the shoulder 53 holds the balls outwardly in the recess so thatthe downward force of the spring 22 on the ball retainer 51 istransmitted through the balls to the lower end surface of the annularrecess 54 in the vaive housing rather than applying the force to thevalve operator piston.

The velocity safety valve 10 remains closed until the pressuredifferential across the valve operating piston is reduced to a valuewhich permits the spring 23 to reopen the valve. The valve is opened byraising the tubing pressure above the valve. When the pressure is raisedin the tubing above the valve, the downward force resulting from suchpressure increase is applied to the top of the valve member 13 at theseat 32. This pressure increase must be sufficient to reduce the pressure differential across the operating piston 12 to a sufficient levelthat the downward force of the spring 23 will initiate the opening ofthe safety valve. It will be recognized that the valve is in thecondition illustrated in FIG. 2 and the lower detent spring 22 is atthis stage in the valve operation disengaged from the operator piston.Depending upon the characteristics of the springs and the extent towhich they are compressed by selective use of the particular spacerrings employed, it may be necessary to raise the pressure within thetubing above the valve to a value at which the pressures are equalizedacross the operator piston. At any rate, when the pressure is increasedabove the valve in the tubing to a value sufficient to permit the spring23 to start downward movement of the valve, the integral valve memberand piston rod are forced downwardly by the spring 23 with the valvemember surface 31 moving downwardly away from the seat 32 to againpermit upward flow through the safety valve through the side ports 21.As the operator piston moves downwardly and the shoulder surface 53 isrealigned with the re' lease recess 54 of the valve housing and with thelocking balls 52, the balls may move inwardly out of the recess 54around the piston head side wall surface above the shoulder 53. Thedownward force of the spring 22 on the ball retainer 51 as appliedthrough the balls to the bottom surface of the recess 54 causes theballs to be cammed inwardly around the piston head above the shoulder 53so that the balls may now pass within the housing bore below the recess54 releasing the engagement of the spring and balls with the housing andreengaging the spring with the operator piston. The additional forceexerted by the compressed spring 22 is coupled with the operator pistonand in combination with the force of the spring 23 snaps the operatorpiston and valve member 13 downwardly to the fully open position of FIG.1 at which the tapered surface 62 on the valve member is seated on thehousing shoulder surface 61.

With the flow restored through the valve, the springs 22 and 23 hold thevalve open until once again the flow rate is increased to a sufficientlyhigh level that the pressure drop through the flow bean 15 ascommunicated downwardly through the tube 20 into the annular chamberaround the operator piston within the valve housing reaches a valuerelative to the well pressure below the valve that the valve is againmoved upwardly to the closed position as previously discussed.

During the upward and downward movement of the valve operator piston,the self-centering seal assembly 63 remains in sealing engagement withthe housing shoulder surface 40 and the outer wall surface of the pistonrod 12a maintaining an effective seal between the housing and theoperator piston. This particular feature provides an effective seal withthe lower manufacturing costs of a seal assembly which may be fabricatedwith greater tolerances since a perfect fit is not necessary between thehousing and the operator piston rod.

It will be recognized that the opening and closing characteristics ofthe valve may be varied by changes in the springs 22 and 23, the spacerrings 42 and 50 as sociated with the springs determining the initialcompression on the springs, and the size of flow bean used. If it isdesired that the valve close at a higher rate, a larger diameter flowbean may be employed along with or alternatively thicker spacer ringsand/or stronger springs. Similarly, if it is desired that the valveclose at a lower flow rate weaker springs, thinner spacer rings, or asmaller diameter flow bean be installed in the valve.

The flow of the well fluids into the valve above the operating mechanismof the valve protects the valve from trash and flow cutting sandreducing malfunction and damage. The larger pressure responsive areapermits operation at lower pressure differentials. The location of theinlet ports and the flow bean allows higher volumes to be handled by thevalve.

What is claimed is:

l. A well safety valve comprising: a valve housing having a bore andadapted for connection with means for supporting said safety valve in atubing string; said housing having ports for admission of well fluids tosaid bore; means defining a valve seat around said bore on a first sideof said ports in said housing; flow rate responsive pressure reducingmeans in said housing on the opposite side of said valve seat from saidports; a valve member movable in said housing and engageable with saidvalve seat for shutting off flow through said bore from said ports; avalve operator piston connected with said valve member and movable insealed relationship in said housing; said operator piston having a firstportion thereof exposed to well fluid pressure; passage means extendingto the low pressure side of said flow rate pressure reducing means forcommunicating a flow rate related reduced fluid pressure to an oppositesecond side of said operator piston for applying a flow rate relatedpressure differential across said piston for closing said piston whenthe well fluid flow rate through said valve exceeds a predeterminedvalue; and means for biasing said operator piston in a direction to opensaid valve.

2. A well valve in accordance with claim 1 wherein said means forcommunicating said reduced pressure comprises a tube communicating atone end with said second side of said operating piston and extendingthrough said means for reducing the pressure in fluids flowing throughsaid valve.

3. A well valve in accordance with claim 2 wherein said tube connectsinto said valve member and extends in said housing bore through saidvalve seat and said pressure reducing means.

4. A well valve in accordance with claim 3 wherein said means forbiasing said operator piston in a valve open direction comprises aspring engaged between said operator piston and said housing.

5. A well valve in accordance with claim 4 wherein an annular chamber isdefined within said housing around said operator piston, said chambercommunicating with said tube extending through said pressure reducingmeasn means applying said reduced pressure to said second side of saidoperator piston.

6. A well valve in accordance with claim 5 wherein said sealed portionof said operator piston closes one end of said annular chamber andincluding a self centering annular seal assembly positioned within saidhousing around a reduced portion of said operator piston closing anopposite end of said annular chamber.

7. A velocity type well safety valve comprising: a housing having a boretherethrough, said housing having ports for admitting well fluids tosaid bore; means defining an annular valve seat within said housingtoward a first end of said housing from said side ports; a pressurereducing flow bean within said housing on the opposite side of saidvalve seat from said side ports; an internal annular flange in saidhousing providing a first stop shoulder facing said side ports and asecond stop shoulder facing a second open end of said housing; a valvemember movably disposed in said bore of said housing between said valveseat and said flange for controlling flow of well fluids from said sideports into said housing bore through said valve seat, said valve memberbeing movable between a first closed position engaging said valve seatand a second open position spaced from said valve seat; a piston rodconnected at a first end with said valve member in said bore of saidhousing extending from said valve member toward said second end of saidhousing; an operator piston connected with a second end of said pistonrod and slidable in sealed relationship along an inner wall surface ofsaid bore of said housing; a self-centering seal assembly concentricallydisposed between said housing bore wall surface and said piston rodsecured against said first stop shoulder of said flange in said housing;said housing and said piston rod and piston being in a concentric spacedrelationship defining an annular chamber within said housing around saidpiston rod and piston sealed towards second end of said housing by saidpiston and toward said first end of said housing by said selfcenteringseal assembly; said valve member and said piston rod having a flowpassage communicating through the end surface of said valve memberfacing said first end of said housing and through a side wall of saidpiston rod into said annular chamber between said rod and said housing;a pressure sensing tube connected into said valve member flow passageextending from said valve member through said flow bean to the oppositeside of said flow bean from said valve seat for communicating reducedpressure from downstream of said flow bean into said annular chamberwhereby the portion of said piston facing said annular chamber isexposed to the reduced pressure downstream of said flow bean and theportion of said piston facing away from said annular chamber is exposedto well fluid pressure through said second open end of said housing; afirst spring within said annular chamber engaged between said secondstop shoulder within said housing and said piston biasing said piston,piston rod, and valve member in a direction to open said valve; anddetent means engaged between said housing and said piston for holdingsaid valve open until a force on said valve assembly is sufficient todisengage said detent means and compress said first spring to close saidvalve.

8. A valve in accordance with claim 7 wherein said self-centering sealcomprises an annular ring having an outside diameter sufficiently lessthan the diameter of the bore of said housing to permit said ring tomove laterally as said piston rod reciprocates through said ring,

said ring having an internal annular recess around the bore through saidring and an annular recess opening through the end face of said ringengageable with said first stop shoulder in said housing; a ring sealwithin said annular recess around said bore of said ring for sealingbetween the bore wall of said ring and said piston rod; a ring seal insaid recess in said end face of said ring for sealing between said ringand said first stop shoulder in said housing; and lock ring meansengaged in said housing around said housing bore holding said sealassembly against said first stop shoulder in said housing.

9. A valve in accordance with claim 8 wherein said detent means includesa second spring within said annular chamber between said housing andsaid piston; said housing having a third internal shoulder facing saidsecond end of said housing; means engaging one end of said second springwith said third shoulder of said housing; a tubular locking ballretainer in said annular chamber engaged with the other end of saidsecond spring; a plurality of locking balls disposed in said annularchamber between said piston and said housing; said housing having aninternal annular locking ball release recess having a tapered camsurface near said second end of said housing for camming said ballsinwardly around said piston out of said release recess; and said pistonhaving a locking shoulder defining a cam surface for engagement by saidlocking balls when said piston cam surface is moved in said housingtoward said second end of said housing for applying a compressive forcefrom said second spring to said piston, said spring urging said lockingballs into locking relationship with said piston when said cam surfaceon said piston is located between said release recess of said housingand said second end of said housing, and said spring being disengagedfrom said piston when said piston is moved away from said second end ofsaid housing to cam said balls outwardly into said release recess andsaid cam surface on said piston is positioned on the opposite side ofsaid release recess from said second end of said housing.

1. A well safety valve comprising: a valve housing having a bore andadapted for connection with means for supporting said safety valve in atubing string; said housing having ports for admission of well fluids tosaid bore; means defining a valve seat around said bore on a first sideof said ports in said housing; flow rate responsive pressure reducingmeans in said housing on the opposite side of said valve seat from saidports; a valve member movable in said housing and engageable with saidvalve seat for shutting off flow through said bore from said ports; avalve operator piston connected with said valve member and movable insealed relationship in said housing; said operator piston having a firstportion thereof exposed to well fluid pressure; passage means extendingto the low pressure side of said flow rate pressure reducing means forcommunicating a flow rate related reduced fluid pressure to an oppositesecond side of said operator piston for applying a flow rate relatedpressure differential across said piston for closing said piston whenthe well fluid flow rate through said valve exceeds a predeterminedvalue; and means for biasing said operator piston in a direction to opensaid valve.
 2. A well valve in accordance with claim 1 wherein saidmeans for communicating said reduced pressure comprises a tubecommunicating at one end with said second side of said operating pistonand extending through said means for reducing the pressure in fluidsflowing through said valve.
 3. A well valve in accordance with claim 2wherein said tube connects into said valve member and extends in saidhousing bore through said valve seat and said pressure reducing means.4. A well valve in accordance with claim 3 wherein said means forbiasing said operator piston in a valve open direction comprises aspring engaged between said operator piston and said housing.
 5. A wellvalve in accordance with claim 4 wherein an annular chamber is definedwithin said housing around said operator piston, said chambercommunicating with said tube extending through said pressure reducingmeasn means applying said reduced pressure to said second side of saidoperator piston.
 6. A well valve in accordance with claim 5 wherein saidsealed portion of said operator piston closes one end of said annularchamber and including a self-centering annular seal assembly positionedwithin said housing around a reduced portion of said operator pistonclosing an opposite end of said annular chamber.
 7. A velocity type wellsafety valve comprising: a housing having a bore therethrough, saidhousing having ports for admitting well fluids to said bore; meansdefining an annular valve seat within said housing toward a first end ofsaid housing from said side ports; a pressure reducing flow bean withinsaid housing on the opposite side of said valve seat from said sideports; an internal annular flange in said housing providing a first stopshoulder facing said side ports and a second stop shoulder facing asecond open end of said housing; a valve member movably disposed in saidbore of said housing between said valve seat and said flange forcontrolling flow of well fluids from said side ports into said housingbore through said valve seat, said valve member being movable between afirst closed position engaging said valve seat and a second openposition spaced from said valve seat; a piston rod connected at a firstend with said valve member in said bore of said housing extending fromsaid valve member toward said second end of said housing; an operatorpiston connected with a second end of said piston rod and slidable insealed relationship along an inner wall surface of said bore of saidhousing; a self-centering seal assembly concentrically disposed betweensaid housing bore wall surface and said piston rod secured against saidfirst stop shoulder of said flange in said housing; said housing anDsaid piston rod and piston being in a concentric spaced relationshipdefining an annular chamber within said housing around said piston rodand piston sealed towards second end of said housing by said piston andtoward said first end of said housing by said self-centering sealassembly; said valve member and said piston rod having a flow passagecommunicating through the end surface of said valve member facing saidfirst end of said housing and through a side wall of said piston rodinto said annular chamber between said rod and said housing; a pressuresensing tube connected into said valve member flow passage extendingfrom said valve member through said flow bean to the opposite side ofsaid flow bean from said valve seat for communicating reduced pressurefrom downstream of said flow bean into said annular chamber whereby theportion of said piston facing said annular chamber is exposed to thereduced pressure downstream of said flow bean and the portion of saidpiston facing away from said annular chamber is exposed to well fluidpressure through said second open end of said housing; a first springwithin said annular chamber engaged between said second stop shoulderwithin said housing and said piston biasing said piston, piston rod, andvalve member in a direction to open said valve; and detent means engagedbetween said housing and said piston for holding said valve open until aforce on said valve assembly is sufficient to disengage said detentmeans and compress said first spring to close said valve.
 8. A valve inaccordance with claim 7 wherein said self-centering seal comprises anannular ring having an outside diameter sufficiently less than thediameter of the bore of said housing to permit said ring to movelaterally as said piston rod reciprocates through said ring, said ringhaving an internal annular recess around the bore through said ring andan annular recess opening through the end face of said ring engageablewith said first stop shoulder in said housing; a ring seal within saidannular recess around said bore of said ring for sealing between thebore wall of said ring and said piston rod; a ring seal in said recessin said end face of said ring for sealing between said ring and saidfirst stop shoulder in said housing; and lock ring means engaged in saidhousing around said housing bore holding said seal assembly against saidfirst stop shoulder in said housing.
 9. A valve in accordance with claim8 wherein said detent means includes a second spring within said annularchamber between said housing and said piston; said housing having athird internal shoulder facing said second end of said housing; meansengaging one end of said second spring with said third shoulder of saidhousing; a tubular locking ball retainer in said annular chamber engagedwith the other end of said second spring; a plurality of locking ballsdisposed in said annular chamber between said piston and said housing;said housing having an internal annular locking ball release recesshaving a tapered cam surface near said second end of said housing forcamming said balls inwardly around said piston out of said releaserecess; and said piston having a locking shoulder defining a cam surfacefor engagement by said locking balls when said piston cam surface ismoved in said housing toward said second end of said housing forapplying a compressive force from said second spring to said piston,said spring urging said locking balls into locking relationship withsaid piston when said cam surface on said piston is located between saidrelease recess of said housing and said second end of said housing, andsaid spring being disengaged from said piston when said piston is movedaway from said second end of said housing to cam said balls outwardlyinto said release recess and said cam surface on said piston ispositioned on the opposite side of said release recess from said secondend of said housing.